Bonded abrasive articles generally are characterized by a three dimensional structure in which abrasive grain is held in a matrix or bond. In some cases the bond is an organic bond, also referred to as a polymeric or resin bond. Organic bonded tools, however, often perform poorly under wet grinding conditions. Wet grinding strength retention is particularly poor in the case of some tools formed of alumina-based grain held in phenolic resin bonds. Abrasive wheels that include phenolic resin bonded abrasive grain designated as “38A” grain, for example, are known for rapid wheel wear in wet grinding, due, it is believed, to the highly water sensitive surface chemistry, i.e., rich Na2O content, in this type of abrasive grain. In the presence of water-based grinding fluid, unspent abrasive grain is prematurely released from the bond.
In one attempt to improve the wet performance of abrasive tools employing phenolic resin bonds, abrasive grains are treated with silanes, thereby rendering the grains hydrophobic. As reported, however, in U.S. Pat. No. 5,042,991, to Kunz, et al., this technique is accompanied by manufacturing difficulties and the improved performance of the grain diminishes after a few months of storage.
In another approach, disclosed in U.S. Pat. No. 3,323,885, wheel life is improved by preventing premature loss of useable grain from the bond; moisture is provided throughout the mass of a green wheel at the initial stage of the curing process, i.e., a relative humidity of at least 20% is maintained for at least five minutes at about 100° C. As the means for providing this relative humidity, the green wheel is wrapped in a moisture impermeable film prior to curing. While the resulting wheels have improved wheel life, the steps of wrapping and unwrapping each wheel add to the manufacturing cost of bonded abrasive tools. In addition, the film prevents the escape of undesirable reaction products, such as ammonia, which remain trapped within the body of the finished article. In the absence of wrapping, water vapor is driven off and evaporates as the green body is heated above 100° C.
Therefore, a need exists for organic bonded abrasive articles and methods of producing them that reduce or minimize the above-mentioned problems.